List of Tables
Chapter 2 Review of Literature
2.9 Impact of climate change on growth and yield of rice
When temperatures exceed the optimal for biological processes, crops often respond negatively with a steep decline in net growth and yield (Rosenzweig and Hillel 1995).
Extreme temperatures whether low or high, cause injury to rice plant. For delineating
specific time periods suitable for maximal production of rice at a given location, it is necessary to know the cardinal (high, low and optimal) temperature requirements of various rice growth stages. From the literature cited by Yoshida (1977), WMO (1983) and Venkataraman (1987), the low, high and optimal temperature requirements for important rice growth stages are given in Table 2.1.
Table 2.1 Temperature requirement for important growth stages of rice
Growth stages Critical temperature/cardinal temperature (°C)
Low High Optimum
Germination 10 45 20 to 35
Seedling emergence 12 35 25 to 30
Transplanting >8 – –
Rooting 16 35 25 to 28
Leaf emergence and elongation 7 45 30 to 35
Tillering 16 33 25 to 31
Flower initiation 15 – 24 to 29
Anthesis 22 35 30 to 33
Ripening 12 >30 20 to 25
Depending on varieties, rice requires a mean temperature above 20°C throughout the growing period (Venkataraman and Krishnan 1992). The optimum air temperature range required for vegetative growth is between 25°C and 30°C. Extreme high temperatures during vegetative growth reduce tiller number and plant height and negatively affect panicle and pollen development, thereby decreasing rice yield potential (Yoshida 1981).
Exposure to high temperatures (>35°C) can greatly reduce pollen viability and cause irreversible yield loss because of spikelet sterility (Matsui et al. 2001). Temperatures above the optimum (20–25°C) shorten the grain-filling period and reduce final yield (Yoshida 1981). In warm temperate/tropical regions depending on variety, local climate, growing season, soil moisture retention capacity and percolation losses, total water requirement in field from planting till harvesting varies from 800 mm to 1800 mm (Kakde 1985). Solar radiation becomes critical for a period of six weeks starting with the panicle initiation stage up to about eight days before maturity (Pal et al. 1996).
The simulations by different crop models and many field experiments have shown the potential impact of climate change and the variability on rice productivity. In a major
study, Mathews et al. (1995) used the ORYZA1 and SIMRIW crop simulation models to predict changes in rice production for all the major rice producing countries in Asia under three different climate change scenarios. In general, an increase in CO2 level was found to increase yields while increases in temperature reduce yields. From that experiment decline in rice yield were predicted under the Goddard Institute of Space Studies (GISS) and United Kingdom Meteorological Office (UKMO) scenarios for Thailand, Bangladesh, southern China and western India; while yield increases were predicted for Indonesia, Malaysia, Taiwan, parts of India and China.
Peng et al. (2004) analyzed weather data at the International Rice Research Institute (IRRI) farm from 1979 to 2003 to examine the temperature trends and the relationships between rice yields and temperature. Annual mean maximum and minimum temperatures increased by 0.35 and 1.13°C, respectively, for the above period and a close correlation between rice grain yield and mean minimum temperature was observed. They concluded that the grain yield declined by 10% for each 1°C increase in minimum temperature in the dry season whereas the effect of maximum temperature was insignificant. Subsequently, a reanalysis of the data from that study, Sheehy et al. (2006) concluded that the actual impact of minimum temperature was much smaller, because minimum temperature was negatively correlated with radiation, thus confounding the observed impact of minimum temperature with the omitted impact of radiation. Lobell (2007) also found that rising of maximum temperature was more harmful to rice yields than minimum temperature in most countries, which contradicts the major negative effect of minimum temperature inferred by Peng et al. (2004). These arguments indicated that current understanding of the impact of temperature on crop yield is still uncertain.
There have been some studies in India aimed at understanding the nature and magnitude of gains and/or losses in yield of rice crop at selected sites under climate variability and change (Sinha and Swaminathan 1991; Abrol et al. 1991; Aggarwal and Sinha 1993; Rao and Sinha 1994; Hundal and Kaur 1996; Lal et al. 1998; Rathore et al. 2001; Mall and Aggarwal 2002; Subash and Ram Mohan 2012). Sinha and Swaminathan (1991) estimated that a 2°C increase in mean temperature could decrease rice yield by about 0.75 ton/ha in the high yield areas and by about 0.06 ton/ha in low yield coastal regions of India. Hundal
and Kaur (1996) examined climate change impact on productivity of rice in Punjab using CERES–rice model. They concluded that, if all other climate variables were to remain constant, temperature increase of 1°, 2° and 3°C from present day condition would reduce grain yield of rice by 5.4%, 7.4% and 25.1%, respectively. In general, the simulation results indicated that increasing temperature and decreasing radiation levels pose a serious threat in decreasing growth and yields of cereal crops (Hundal and Kaur 1996). Lal et al.
(1998) examined the vulnerability of rice crop in northwest India to climate change and found that under elevated CO2 levels, yield of rice increased significantly by 15% for a doubling of CO2. However, a 2°C rise in temperature cancelled out the carbon fertilization effect. Analyzing the effect of climate change (increase in monsoon season mean temperature of the order of 1.5°C, an increase rainfall of the order of 2 mm per day and CO2 460 ppm) on rice crop over the Kerala state, Saseendran et al. (2000) showed that the rice maturity period was shortened by 8% and yield increased by 12%. They demonstrated that when temperature elevations only are taken into consideration, the crop simulations showed a decrease of 8% in crop maturity period and 6% in yield. They also showed that for every one degree rise in temperature, the decline in rice yield would be about 6% over the state.
Aggarwal and Mall (2002) studied the impact of various climate change scenarios on grain yield of rice using CERES–Rice and ORYZA1N at different levels of management in different regions of India (North, West, South and East). Increase of 1° to 2°C temperature without any increase in CO2 resulted in a 3% – 17% decrease in grain yield in different regions. In general, as the temperatures increased, rice yields in eastern and western India were less affected, moderately affected in north whereas severely affected in southern India. Grain yields increased in all regions as the CO2 concentration increased. A doubling of CO2 resulted in 12% to 21% increases in yield in different regions. They also showed that the beneficial effect of 450 ppm CO2 was nullified by an increase of 1.9° – 2.0°C in northern and eastern regions and by 0.9° – 1.0°C in southern and western regions.
Pathak et al. (2003) studied trends of climatic potential yields and on-farm yield rice in the Indo–Gangetic Plains using the DSSAT model (CERES−Rice). Negative yield trends were observed at six of the nine sites, four of which were statistically significant (P < 0.05). The
decrease in radiation and increase in minimum temperature were identified as the reasons for the yield decline. They showed that solar radiation decrease by 1.7 MJ/m2/day reduced rice yield from 10.9 to 10.3 ton/ha. Increase in minimum temperature by 1.7°C decreased yield of rice from 10.9 to 10.0 ton/ha.
Krishnan et al. (2007) simulated the impact of CO2 and temperature on rice yield (variety IR 36) at 10 different sites of eastern India using the ORYZA1 and the INFOCROP rice models. In general, for every 1°C increase in temperature, the ORYZA1 and INFOCROP rice models predicted average yield changes of –7.2% and –6.6% respectively at the current level of CO2 (380 ppm). But considerable differences in the yield predictions under three GCM scenarios (GFDL, GISS and UKMO) were observed for individual sites, with maximum declining trend for Cuttack and Bhubneswar but an increasing trend only for Jorhat. These differences in yield predictions were mainly attributed to the sterility of rice spikelets at higher temperatures. For instance, Cuttack and Bhubaneswar had high maximum temperature of about 34°C and minimum temperature of 25°C during the flowering period. But Jorhat had the maximum temperature of about 28°C and a minimum temperature of 19°C only, which probably contributed to the benefits from the predicted effects of climate change scenarios (Krishnan et al. 2007). Recently, Kumar et al. (2011) reported the results of simulation analysis (using INFOCROP model) on various crops in NE India and inferred that climate change may bring changes in irrigated rice yields by about –10% and 5%, while in the rain-fed rice are likely to be in the range of –35% to 5%
in A1B 2030 climate scenarios.